1. Field of the Invention
The subject invention pertains to flexible polyurethane foams and polyol compositions suitable for their preparation. More particularly, the subject invention pertains to the preparation of polyurethane foams having higher resistance to burning through incorporation of a minor quantity of a low molecular weight, high primary hydroxyl content polyether polyol into the polyol component of the polyurethane reactants.
2. Description of the Related Art
Polyurethane flexible foams are well established commercial products having uses in seat cushions; carpet underlay; mattresses; automobile dashboards, arm rests, head rests; and like applications. An important consideration when employing polyurethane or other polymeric foams is the ability of such foams to resist ignition, or once ignited, to be self-extinguishing when the ignition heat source is removed. This is especially important when the foam is to be used within confined spaces such as homes, buildings, hospitals, airplanes, trains, and cars, for example.
Attempts to decrease the flammability of polyurethane foams have taken many paths. Halogenated flame retardants such as the halogenated alkyl phosphates and perhalogenated hydrocarbons such as decabromodiphenyloxide have been added to foam formulations. Unfortunately, such flame retardants are relatively expensive; pose environmental problems, particularly with regard to potential spills and disposal of scrap or used foam products; may alter foam properties in an unacceptable manner; and finally, provide only a limited amount of improvement with regard to flammability.
Foams filled with large amounts of nitrogenous substances have been proposed. Addition of large amounts of urea has been found to decrease the flammability of polyurethane foams, however the foam physical properties are far less than ideal. Moreover, the urea in largest part does not react with the foam-forming ingredients, and being soluble, can leach out of the foam during use, not only increasing flammability, but also rendering the foam unsuitable for many applications. Melamine has been added to polyurethane foams, and foams containing from 30 to 55 parts by weight melamine have proven to be highly flame retardant. However, melamine also reduces foam physical properties, as well as resulting in a "heavy" foam product. Furthermore, unless crushed or ground to exceptionally fine particle sizes, melamine/polyol dispersions are unstable, the melamine sedimenting out upon storage. Lower amounts of melamine, i.e. 5 weight percent, do not cause substantial loss of foam physical properties and may even decrease the compression set of flexible foams. However, this low level does not provide sufficient flame retardancy for many applications.
The use of graphite or combinations of graphite and melamine has also been proposed, however the foams and their processing share many of the same defects associated with melamine filled foams discussed previously, Other solid flame retardants such as aluminum oxide, alumina trihydrate, antimony compounds, and the like have also been proposed. Such flame retardants are expensive, and result in very "heavy" foams not having optimal physical properties.
The use of acrylonitrile/styrene graft polymer polyol dispersions has resulted in polyurethane foams with improved physical properties together with a minor decrease in flammability. Use of such dispersions, and also dispersions of polyisocyanate addition products, in conjunction with melamine has been commercialized. Again, however, at low melamine levels flame retardancy is not adequate for many applications.
It would be desirable to enable preparation of polyurethane foams displaying decreased flammability and increased self extinguishing properties without recourse to the use of solid fillers such as those described previously. It would further be desirable to further decrease the flammability of foams prepared with such fillers or decrease the amount of filler for a given level of flame retardancy. It is further desirable to achieve the above results without recourse to expensive foam raw materials and without developing problems with respect to foam formulation and/or processing.